Hexane biodegradation in two-liquid phase bioreactors: High-performance operation based on the use of hydrophobic biomass

An innovative operation mode in two-liquid phase bioreactors (TLPB) for the treatment of volatile organic compounds (VOC) was investigated. This mode was based on confining the biocatalytic activity exclusively in the non-aqueous phase (NAP) by using hydrophobic microorganisms. The TLPB was implemented in a 2.5 L stirred tank reactor using 10% (v/v) of silicone oil as NAP and hexane as model VOC. A stable elimination capacity (EC) of 21.0 ± 2.5 g m^?3 h^?1 (corresponding to a removal efficiency of 80%) was recorded for 26 days. The accumulation of inhibitory metabolites resulted in drastic drops in the elimination capacity (EC) and an unstable performance of the system, hexanol being identified as potential inhibitory metabolite. Aqueous culture broth exchange by fresh mineral salt medium at a dilution rate of 0.2 day^?1 allowed maintaining a high and sustained VOC removal performance. Dissolved oxygen concentration measurements revealed that the oxidative metabolism was strongly stimulated by the aqueous broth exchange. The temporary blockage of the gas/water/NAP transfer pathway for O₂ highlighted the paramount role of this pathway on the performance of the TLPB based on hydrophobic microorganisms.